Perforated films are typically used in the personal hygiene field providing a fluid transfer film allowing the fluid to be removed from areas near to the skin and into the absorbent area. Other common applications are in the food packaging industry and more recently acoustics absorption. Perforated films for these applications are usually less than 100 micrometers (0.004 inch) thick (more typically less than 50 micrometers (0.002 inch) thick) and are made, for example, of olefins, polypropylene, or polyethylene.
Typical processing methods to produce perforated films include; vacuum drawing of film into a perforated panel or roll, use of pressurized fluid to form and puncture the film, needle punching with either cold or hot needles, or lasers to melt holes in the film. These processes, however, tend to have processing limitations such a hole size, hole density, and/or film thickness of film.
Vacuum or pressurized fluid forming of perforated films tends to be limited to relatively thin films (i.e., films less than 100 micrometers thick) due to the forces available to deform and puncture the film. Also materials used in this type of forming process tend to be limited to olefin-based polymers. Another characteristic of this type of process is the creation of a protrusion in the film where the film is stretched until a perforation is created. This protrusion can be an advantage in the case of fluid control where the protrusion can act as a directional flow control feature. However, it can also be a disadvantage in applications where a low pressure drop is desired. The protrusion creates an elongated hole thereby increasing the surface area and increase fluid drag.
Needle punching processes are also largely used for relatively thin films, but film thicknesses up to about 254 micrometers (0.010 inch) are sometimes seen. Limitations with this process tend to include perforation diameter holes per unit area, and protrusions in the film.
Laser perforation processes can provide relatively small holes (i.e., less than 50 micrometers), can perforate a wide range of thicknesses, can create perforations that are planar with the film surfaces (i.e., without the protrusions associated, for example, with needle punching processes). Limitations of laser perforation processes include the types of materials that suitable for the process, and processing speeds and costs. Laser perforation processes tend to be best suited for processing films from polyethylene terephthalate (PET), polyethylenenaphthalate (PEN), polycarbonate (PC), or other higher glass transition temperature materials. Lasers are often not very effective, for example, in perforating olefin-based materials.